Injection height impact on combustion instability in a centrally staged combustor

Centrally staged lean premixed pre-vaporized (LPP) combustors are widely applied in aeroengines to reduce pollutant emissions. However, combustion instability represents a critical challenge in the development of it. In the centrally staged combustor, injection height is defined as the injector-wall distance of the main stage. The partially premixed swirling combustor was built to study the effect of injection height on combustion instability, and several schemes under various conditions were investigated. Spray fields corresponding to different configurations were measured in cold flow, and reactive experiments were conducted in different equivalence ratios of the main stage (φm). The results indicate that combustion instability occurred in conjunction with stratified flames. The injection height mainly affected the amplitude of the combustion instability. It affected the heat release fluctuations and the phase difference between the heat release and pressure fluctuations by influencing the flame structure, which finally affected the oscillation. Dynamic mode decomposition analysis showed that oscillations in three cases occurred within the axial modes; however, a reduction in injection height slightly decreased the resonant frequency. These results have rarely been reported in previous work and may provide useful ideas for designing LPP combustors.